The mainstream centrifugal fans employ non-twisted two-dimensional blades provided between a main plate and a shroud. Thus, the main plate and the blades are typically integrated. However, to further reduce noise and power consumption, twisted three-dimensional blades that are provided between the main plate and the shroud have become necessary.
A three-dimensional blade can be formed in a complex shape with an increased flexibility in resin molding by using a plurality of parts for the blade. In addition, the blade is formed to have a hollow internal structure so as to achieve a lightweight configuration (see, for example, Patent Literature 1).
In another example, in an engagement portion in which a plurality of parts constituting a three-dimensional blade of an axial flow fan engage with each other, an engagement line formed between these parts by their engagement bends in a zigzag pattern and bent portions are joined to each other by local irradiation with an ultrasonic wave in order to increase the number of joints, and thereby enhance the strength of joint (see, for example, Patent Literature 2).